Nearly 200 years of information on acetate microfilm

May 24, 2018

Many federal agencies maintain archives of historical data that are recorded on media that is becoming—or already is—obsolete. Federal librarians are grappling with preserving media like acetate microfilm and nitrate film. Without these preservation efforts, we could lose historical data that has relevance today.

At the National Oceanic and Atmospheric Administration (NOAA), a core part of its mission is to understand and predict changes in climate, weather, oceans, and coasts. Of course, the ability to predict the future depends on analysis of historical trends using data that NOAA’s predecessor agencies have collected for nearly 200 years. From the 1920s to the 1980s, some of that data was stored on acetate-based microfilm.

As our team discovered during a recent project, NOAA’s microfilm collection contains global weather and wind data that could be crucial in today’s studies of climate change. Some data goes back as far as 1862, and Antarctic weather data starts in 1928. This valuable information provides a snapshot of climate conditions and forms the basis for tracking variations and determining patterns.

The challenge of acetate film degradation

Like any physical substance, film degrades over time. Acetate film deteriorates through a chemical process called acetate base decay, or “vinegar syndrome.” According to the National Film Preservation Foundation, “The symptoms of vinegar syndrome are a pungent vinegar smell (hence the name), followed eventually by shrinkage, embrittlement, and buckling of the gelatin emulsion. Storage in warm and humid conditions greatly accelerates the onset of decay. Once it begins in earnest, the remaining life of the film is short because the process speeds up as it goes along. Early diagnosis and cold, moderately dry storage are the most effective defenses.”[1]

Vinegar syndrome carries additional risks, including health hazards to people handling the film without protective gear. The decay process results in the release of acetic acid which can be corrosive to skin, eyes and mucous membranes and dangerous if inhaled. Dizziness and lightheadedness can occur, especially if the work area is not properly ventilated.

Once the process begins in a collection, it can spread from film to film because of the gaseous emission. This is why it is particularly critical to detect it early and contain it through proper storage before the entire collection is lost.

Assessing NOAA’s acetate microfilm collection

During our project at NOAA, I worked with librarians to identify the state of the acetate microfilm collection and make recommendations based on our findings of its condition. Our team also addressed other challenges facing the NOAA acetate film library, including:

The microfilm collection was mostly uncatalogued

The finding aid was incomplete

The film was not organized in an intuitive fashion

In short, in addition to issues of decay, it was difficult to know exactly what was in the collection, therefore no one knew what could be lost if nothing was done.

We started by assessing the levels of degradation using A-D strips. These are essentially paper strips that are coated with a dye that reacts in the presence of the acidic vapor given off by decaying film. Items should be in a closed container with the A-D strip for a length of time determined by storage conditions. At room temperature, it takes 24 hours to get an accurate reading on the strip.

A-D strips used to determine the current state of acetate base decay of microfilm. Photo by Jennifer Fagan-Fry.

A-D strips react by changing color according to the level of severity of the decay. The guidance that we followed came from the Image Permanence Institute [2]:

Image from Permanence Institute Chart 2017.

There were eight cabinets of microfilm, and we decided to begin by randomly choosing two drawers in each cabinet to test at the drawer level, with the exception that we tested every drawer in Cabinet 2, which was known to house some of our most problematic items, and only one drawer each in Cabinets 7 and 8, since those cabinets were less than half full. Each drawer can hold up to 60 rolls of microfilm. The results can be seen below.

Based on those results, we decided to test all of the drawers in Cabinet 1, with 7 drawers ranking at level 1, and 2 drawers at level 1.5.

Following our testing, we estimated that approximately three quarters of the collection was at level 0, meaning that no deterioration had yet occurred. The rest of the collection tested at levels 1 to 1.5. Luckily, none of NOAA’s microfilm had yet reached levels 2 or 3.

Assessed the content of the microfilm collection and removed materials outside of scope. Photo by Jamie Roberts.

Since each item in the film collection was being handled, we also took the opportunity to thoroughly document the contents, create a finding aid and remove any items that didn’t belong.

All of the microfilms that showed signs of deterioration were moved to cold storage, and the remaining items will be closely monitored for any future signs of decay. Ideally, every item in the collection will get digitized, but for the short-term, the films are stable, discoverable and their valuable data is preserved.

The project at NOAA is a great example of how important it is to expertly assess and stabilize older acetate films so that their contents will remain available for research and historical purposes. If you have any questions about your historical film collection, please contact us to discuss your needs.

Jamie Roberts

Jamie Roberts is a Librarian at LAC Group supporting the NOAA Central Library. She has been with NCL since 2016 and splits her time between reference services, outreach, and bibliometrics. She earned her M.A. in Principles of Conservation from University College London and her MSLIS from the Catholic University of America.